The proposal deals with two separate lines of investigation both representing continuations of our present program. One deals with the Ca ions transport across sarcoplasmic reticulum membranes, the other with the elementary steps of ATP hydrolysis by myosin. The primary aim of the work on sarcoplasmic reticulum is to define the nature of proteinlipid interactions important in Ca ions transport and ATP hydrolysis. The problem will be approached by quench-flow kinetic, immunochemical, fluorescence and electron spinresonance methods and by differential scanning calorimetry. Developmental changes in the physical properties of membrane phospholipids will be correlated with the changes in the concentration and activity of the Ca ions carrier and with the Ca ions permeability of the membrane. The regulation of the synthesis of transport ATPase will be studied after isolation of its messenger RNA. The possible participation of sarcoplasmic reticulum membranes in lipid biosynthesis will be analysed in developing chicks. The Ca ions transport ATPase will be fragmented with cyanogenbromide and the amino acid composition and sequence of the resulting peptides will be established. The role of proteins and phospholipids in the regulation of the passive Ca permeability of the membrane will be investigated in reconstituted membrane preparations. The correlation between membrane potential and Ca-fluxes will be analysed using fluorescent probes, and attempts will be made to isolate sarcoplasmic reticulum membranes which respond to physiologically effective stimuli with Ca ions release. The principal aim of the studies on contractile proteins is to establish the relationship between binding sites for divalent metal ions, ATP, ADP and actin on skeletal, cardiac and smooth muscle myosins by a combination of rapid kinetic and equilibrium techniques and to further analyse the rates of elementary steps in ATP hydrolysis in relationship to the contraction process.